We will study the conduction system by serial section in cases of sudden death and in cases where His bundle recordings have been done. We will study the course of conduction system in surgically important types of congenital heart disease. We will alter our procedure of studying the conduction system by introducing Holmes Silver Stain of nerves. We will study atrial biopsies by cholinesterase staining to look for specific conduction cells. We will study the conduction system in acromegaly and asymmetrical septal hypertrophy to find out whether conductive cells hypertrophy. We will continue our studies of the conduction system and the A-V communications in congenital A-V block and WPW. We will study the truncus valve and A-V valves in common A-V orifice to distinguish between dysplasia and hemodynamic change. We will study the myocardium in congenital heart disease by strategic sections of inflow, outflow tracts and the septum. We will continue to examine grossly most of the congenital hearts in the Chicago area. We will probe the following complexes grossly--fetal coarctation, complete transposition with pulmonary stenosis, mitral atresia with ventricular septal defect, hemitruncus, aortic atresia with ventricular septal defect, common atrium, and coarctation with vetricular septal defect.